Lead salt rust preventive pigments such as minium, lead cyanamide, and calcium metaplumbate, and metal chromate rust preventive pigments such as basic zinc chromate and strontium chromate had once been the main reagent used for preventing the rust. Use of such reagent, however, was gradually restricted in consideration of the health hazard and environmental conservation. Since then, non-polluting, non-toxic rust preventive pigments have been developed. Exemplary such rust preventive pigments include metal phosphates such as zinc phosphate, calcium magnesium phosphate, titanium phosphate, and silica phosphate; condensed metal phosphates such as aluminum tripolyphosphate; metal phosphorite such as zinc phosphorite, calcium phosphorite, strontium phosphorite, and aluminum phosphorite; zinc molybdate, calcium molybdate, barium borate, and zinc borate. Use of these non-polluting, non-toxic rust preventive pigments did not bring a major change since rust preventive pigments were still used.
JP-A 5-140491 (Patent Document 1) discloses a water-borne etch-resistant coating composition for a metal plate produced by adding a surfactant and an acetylene alcohol compound and/or an acetylene glycol compound. In this coating composition, the resin component is uniformly distributed on the metal surface by the use of a surfactant and the use of an acetylene alcohol compound combined with the acetylene glycol compound, and the etch-resistance is realized by the resin.
JP-A 2000-104015 (Patent Document 2) discloses a thermosetting rust preventive coating composition comprising a water-borne polyurethane resin having the thermosetting property. Use of the urethane resin, however, is associated with the drawback of high cost.